Jet Propulsion Laboratories (JPL) of Pasadena, Calif. introduced a new type if image sensor circuit known as a CMOS image sensor. A CMOS image sensor is an integrated circuit that measures light by detecting a voltage change produced by a photo sensor. Specifically, a photo sensor is charged to a predetermined voltage value and then allowed to integrate by being exposed to a light source. The voltage value of the photo sensor is then read out by a read-out circuit consisting of a transistor.
Existing CMOS image sensors have proved useful for some applications. However, there are problems with existing CMOS image sensors. For example, individual CMOS image sensors in an array do not behave uniformly therefore a CMOS image sensor array must be calibrated with a uniform image, such as a gray plane, before use. The dynamic range of existing CMOS image sensors is limited such that images with large light variation are difficult to capture. Existing CMOS image sensor circuits are highly susceptible to noise problems. Specifically, the read-out of a CMOS image sensor pixel circuit may affect the integration of an adjacent CMOS image sensor pixel circuit. Existing CMOS image sensors also exhibit undesirable nonlinear behavior. Due to the problems associated with existing CMOS image sensor circuits, an improved CMOS image sensor circuit would be desirable.